PROJECT SUMMARY Zika virus (ZIKV) infection in pregnancy is linked to a spectrum of fetal anomalies including microcephaly and other CNS lesions. Male-to-female sexual transmission of ZIKV is well documented. ZIKV transfers to semen and persists much longer vs. blood. Prolonged detection of ZIKV in the vagina and cervical mucus has been noted in humans. Vaginal ZIKV infection of non-pregnant macaques leads to prolonged infection of the female reproductive tract and systemic infection. Thus, the vagina appears to be a favorable environment for ZIKV propagation and infection. The olive baboon's (Papio anubis) similarity to humans in terms of genetics, size, reproductive physiology, placentation and immune repertoire makes this primate an excellent translational model for studying ZIKV infection during pregnancy. Our team has flavivirus experience with the baboon. Our preliminary data show that subcutaneous (sc) ZIKV inoculation during pregnancy can lead to vertical ZIKV transfer to the fetal CNS. We hypothesize that vaginal inoculation of ZIKV infected semen in pregnant baboons will result in 1) prolonged ZIKV persistence in the CV tract and dissemination to the local urogenital lymphatics, including targeting of dendritic cells, macrophages and lymphocytes, enhancing ZIKV transfer to the uterus, 2) activation of a CV mucosal immune and inflammatory response including immune cell migration (monocyte, neutrophil, T cell) into CV tissue, 3) enhanced placental ZIKV infection resulting from enhanced ZIKV infection of the uterus via urogenital lymphatics and/or ZIKV ascension through the cervical canal to the intrauterine compartment and 4) enhanced vertical transmission of ZIKV with a more severe fetal CZS pathology and/or pregnancy loss. We will determine the effect of vaginal inoculation of pregnant baboons with ZIKV-infected semen during early- (50 days gestation, dG), and mid- (90 dG;) gestation on Aim 1) persistence and propagation of ZIKV in the CV tract and spread to the local urogenital lymphatic system, Aim 2) CV innate and adaptive immune responses (immune cell recruitment into CV tissue, CV inflammation, mucosal IgA response) and Aim 3) ZIKV infection and pathology of uterus and vertical transmission placenta and fetus. We will infect early- (50 days gestation [dG]), and mid- (90 dG; term ~181 dG) gestation baboons representing unique periods of primate CNS development with potentially different CNS outcomes. ZIKV infection in early to mid-gestation is linked to most severe fetal CNS outcome in humans. Pregnancies will be terminated near term (170+/1 dG) for tissue collection in one cohort and at 28 days post-onset of maternal ZIKV viremia in a second cohort allowing both acute (cellular/tissue targeting) and chronic maternal-fetal pathological effects of ZIKV to be examined. We will compare outcomes from vaginal infection to our ongoing project using sc route of inoculation as well as to age-matched control pregnancies.